Two types of processes for the production of maleic anhydride graft polyolefin have been already known as follows:
(1) A solution polymerizing process comprising the steps of: dissolving a polyolefin, such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, or the like, in an organic solvent, such as benzene, toluene, xylene, chlorobenzene, or the like, while being heated; and adding dropwise thereto an organic solvent containing maleic anhydride and an initiator, such as dicumyl peroxide, or the like, followed by stirring the solution, thereby making graft polymerization (Japanese Patent Publication Nos. 3254/77 and 15422/69); and PA0 (2) A melt polymerizing process comprising the steps of heating a mixture of the above-mentioned polyolefin, maleic anhydride, and an initiator, followed by mulling the melt by the use of an extruder, thereby making graft polymerization (Japanese Patent Publication No. 39675/81). PA0 (a) A process of removing unreacted maleic anhydride comprising the steps of cooling maleic anhydride graft polyolefin down to room temperature after graft polymerization, washing with acetone, and drying under reduced pressure (Japanese Patent Publication No. 32654/77); PA0 (b) A process of removing unreacted maleic anhydride comprising extracting maleic anhydride from maleic anhydride graft polyolefin with acetone (Japanese Patent Publication No. 15422/69); and PA0 (c) A process of removing unreacted maleic anhydride comprising washing maleic anhydride graft polyolefin by blowing pressurized steam thereto.
The maleic anhydride graft polyolefin obtained by these processes still contains unreacted maleic anhydride which consequently diminishes adhesion of the graft polymer to polyamide, metal, etc. In order to prevent the loss of adhesion, the following types of processes have been proposed:
Of these processes, the processes (a) and (b) using acetone are high in cost, since a part of the acetone (boiling point: 56.5.degree. C.) used is not recovered. The process (c) is not satisfactory for removing unreacted maleic anhydride in the case where the particle size of the modified resin is large. In addition, the incidental equipment required for the process (c) is expensive.